I realized this is an old thread, but I don't know whether you went through with your tattoo or not and this is a good little article I read a while ago and decided to re-find just for this thread,
http://www.ucg.org/bible-faq/why-shouldnt-we-wear-cross-sign-being-christian, now it doesn't have to do with tattoos, but the same principle goes. Also, I highly suggest that you read Romans 14 and specifically pay attention to verses 15-23. I haven't dealt with this question in a while because I made a permanent decision at one point to never get a tattoo after praying to God for the answer to whether it was ok or not and basically and getting my answer, which was "no". It wasn't just a blatant "no", God gave me insight to help me find out not to do it, but I once wanted a tattoo too, for quite a while also. Btw, I didn't get my answer overnight, it took years for me to realize that God didn't want me, or you, or anyone else to get a tattoo. Now I don't think getting a tattoo is some irreversible sin like the mark of the beast, so don't go freaking out if you got one. I just believe getting a tattoo is a sin, and everyone sins, it's in our nature literally. I could keep going and going on this subject and how it leads to countless other subjects but i'm just a messenger and am pretty worn out atm. Just remember to listen to God and he will give you the answers you seek.